Lab talk

Jul 13, 2012

Nanoscale p-n junction improves gas selectivity

Simple oxidative or reductive interactions between the surface of oxide semiconductors and gas molecules often limit the selective detection of a specific gas. Many efforts have been made to improve gas selectivity, which include the manipulation of acid-base properties, the catalytic promotion of gas sensing reaction, and the use of a filtering layer.

In a recent study published in the journal Nanotechnology, researchers at Korea University in Seoul, Korea, have investigated the use of n-type ZnO nanowires decorated with a discrete configuration of p-type Cr2O3 nanoparticles. The team has found that the combination is very promising for detecting trimethylamine (TMA) in a highly selective and sensitive manner.

TMA is secreted from the decay of dead fish and provides a good measure to evaluate their freshness. "The nanowire/nanoparticle sensor could be integrated in a mobile phone or other small portable electronic devices," explained Jong-Heun Lee, who leads the Functional nanostructured materials laboratory.

Enhanced response

The response to TMA of Cr2O3-decorated ZnO nanowires was 17.8, which was 3.3 times higher than prisitine ZnO nanowires. What's more, the selectivity toward TMA was significantly enhanced by the decoration of Cr2O3. This was explained by the catalytic effect of Cr2O3 towards TMA and the extension of the electron depletion layer via the formation of radial p-n junctions.

In further work, the scientists will examine the formation and configurational design of nanoscale p-n junctions using different oxide semiconductors for detecting specific gases. The group also plans to use similar nanoarchitectures to make new LED devices.

About the author

Hyung-Sik Woo and Chan Woong Na are currently PhD candidates in the department of Materials Science and Engineering at Korea University in Seoul, Korea, supervised by Prof. Jong-Heun Lee. Hyung-Sik Woo fabricated and characterized the nanowire sensors. Chan Woong Na supported the vapour phase growth of nanowires. Prof. Il-Doo Kim from the department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Korea, participated in the TEM characterization and discussion. Prof. Jong-Heun Lee is group leader of the functional nanostructured materials laboratory at Korea University. His research interests include functional oxide nanostructures, oxide gas sensors and solid oxide electrolytes.